Blender Git Loki

BMesh: mesh-data picking, general improvements

Generalize logic for vert/edge/face selection:
- index cycling.
- selection bias with mixed modes.

Details:
- Edges now support index cycling (as verts/faces did already)
- Cycling over near elements is now only enabled when the mouse position remains the same.
- No longer do 2 selection passes to perform index cycling.

Fixes:
- Edges behind the view could be selected (surprising nobody reported!)
- Selection bias now only changes the element that gets picked without interning the return distance
(was buggy with mixed modes).